This invention relates, in general, to a semiconductor device package, and more particularly, to an electronic module and a method for coupling a power lead to a bond pad in the electronic module.
Power semiconductor devices are used in a variety of applications, including: electric vehicles, switch mode power supplies, and electric motors such as those used in cooling, heating, and ventilation systems. Since large currents flow through power semiconductor devices, they are generally packaged in modules capable of dissipating large amounts of heat. One type of power semiconductor device module includes a copper baseplate to which an isolation pad is mounted. The isolation pad may include a ceramic layer sandwiched between two thin copper sheets. One of the thin copper sheets is bonded to the copper baseplate which in turn is mounted to a cold plate or a heat sink. Semiconductor die are mounted to the second thin copper sheet.
Bonding pads on the semiconductor die are coupled to power leads by wire bonds. Subsequently, the semiconductor die, the wire bonds, and portions of the power leads are encapsulated by a molding compound. An important feature of this type of packaging scheme is that the wire bonds coupling the die bonding pads to the power leads have a large area to support the high current levels from the power semiconductor devices. Typically, the wire bonds are smaller than the bonding pads and are attached to the die bonding pads using ultrasound.
A major failure mechanism in these types of packaging schemes is that the bond foot, i.e., the location where the wire is connected to the die, may become fatigued and crack. Further, heavy buss bars to which the power modules are mounted can create a large twisting moment on the power leads, thereby creating stresses that may be transferred to the bond foot. Due to the encapsulation and the expansion of the encapsulation material during thermal cycling, wire bonds are pulled and stresses are induced on the wire bonds, thereby increasing the number of failures.
Accordingly, it would be advantageous to have an electronic module and a method for coupling a power lead to a bond pad in the electronic module that increases the reliability of the module. It would be of further advantage for the method to eliminate bond foot fatigue.